Electromagnetic welding techniques are known for joining parts together. However, joining dissimilar metals, for example steel and aluminum, together is generally to be avoided because of the risk of galvanic corrosion. Galvanic corrosion may occur if parts formed of different metals are contacted by an electrolyte.
One way to avoid galvanic corrosion is to electrically insulate the two metals from each other. Unless the parts are in electrical contact, no galvanic coupling is created. Preventing electrical contact can be done using a plastic insert or a protective plastic layer. For example, steel water pipes may be separated from copper-based fittings by an insulating insert. In another example, a coat of grease may be applied to separate aluminum from steel parts. Piping can be isolated by using a plastic pipe or by using a pipe made of metal that is internally coated or lined. However, applying substantial loads to the plastic part or coating should be avoided because these materials usually have low mechanical strength.
Another way to avoid galvanic corrosion is to keep the metals dry or shielded from ionic compounds (salts, acids, bases) that create an electrolyte when in an aqueous solution. For example, a metal part may be painted or encased in plastic or epoxy. Coating the two different metal parts with a protective paint or assembling an insert between the two parts may be effective but adds cost to the manufacturing process. Coatings or epoxy layers can be damaged over the life of the joint allowing galvanic corrosion to initiate.
Electrically insulating by adding plastic layers or inserts, shielding from ionic compounds and coating with protective paints are all approaches that add cost and process steps to the manufacturing process. Applying grease between the parts may work for a while but over an extended period of time the grease may wash off of the parts and the protection against galvanic corrosion may be lost.
The above problems and disadvantages and others are addressed by the disclosed method as summarized below.